In an ordinary liquid crystal display device, a longitudinal electric field system typified by a twisted nematic display system in which an electrode driving a liquid crystal layer held between a pair of substrates is constructed of a transparent electrode formed opposite to each of the pair of substrates and an electric field provided in a direction approximately vertical to the surfaces of the substrates is applied to drive a liquid crystal was employed.
On the other hand, a lateral electric field system in which an electric field applied to a liquid crystal is provided in a direction approximately parallel to surfaces of substrates was developed. As an example of this system, the use of a pair of comb-like electrodes in which an electrode providing an electric field approximately in parallel with the surfaces of the electrodes is formed on one of the substrates is disclosed in, for example, Japanese Patent Publication No. 21,907/1988, U.S. Patent Specification No. 4,345,249, European Patent No. 91/10,936, Japanese Patent Laid-Open Nos. 222,397/1994 and 160,878/1994, and the like. It is unnecessary that the electrodes disclosed in these documents are transparent, and opaque metal electrodes having a high conductivity are used.
In the display system in which the direction of the electric field applied to the liquid crystal is a direction approximately parallel to the surfaces of the substrates as disclosed in the above-mentioned documents, a method for reducing display unevenness present from the outset, such as an edge domain has been proposed to date in Japanese Patent Laid-Open No. 159,786/1995. However, a construction or the like which is required for eliminating display unevenness occurring in a stress test such as a high-temperature working test or the like and improving a productivity is not described at all.
Applicant of the present application has found, with respect to the foregoing liquid crystal display device of the lateral electric field system, that usual AC driving is conducted at a high temperature of 55 DEG C. or the like to form a residual image (this is referred to as an AC residual image) which leads to a display defect.
For eliminating this display unevenness, Applicant of the application has made assiduous effort, and has consequently confirmed that it is not observed so long as the AC residual image is below a certain percentage. And, it has been found that for coping with the display defect caused by the display unevenness, it is effective to use a specific oriented film and increase an interaction between the oriented film and the liquid crystal molecules.
It has been moreover found that a silane coupling agent in the oriented film which is ordinarily used to improve an adhesion with substrates influences the display unevenness.
The invention aims to provide a liquid crystal display device that enables high-quality image display upon eliminating the display defect caused by the AC residual image.